High speed printer addressing apparatus utilizing multi-tapped delay line



May 21, 1968 A. MACOVSKI ET AL 3,334,898

HIGH SPEED PRINTER ADDRESSING APPARATUS UTILIZING MULTI-TAPPED DELAYLINE Filed Dec. 50, 1963 $TATlON pL/ILEJE SOURCE COMPUTER O UT D UT 2450 CRCULATlNC-z MEMORY READER CGMPARATOR ADDRESSlNG CARCLHTIS /36COMPUTER OUTPUT jo CIRCULATING 42 MEMORY PULSE .1

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COM PARATOR ALBERT/#22 95 5 Y 4 BYHL/GH F. FROHBACH A 77'0/8NEY UnitedStates Patent HIGH SPEED PRINTER ADDRESSING APPARATUS UTILIZINGMULTI-TAPPED DELAY LINE Albert Macovski, Palo Alto, and Hugh- F.Frohhach, Sunnyvale, Calif., assignors to Stanford Research Institute,Palo Alto, Calif., a corporation of California Filed Dec. 30, 1963, Ser.No. 334,364 5 Claims. (Cl. 346-74) ABSTRACT OF THE DISCLOSURE Anarrangement for electrostatically printing at a high speed uses a drumhaving type characters arranged in rows around the periphery thereof. Ata printing position spaced from the type characters are a plurality ofaligned electrodes. Paper to be printed on is passed between theelectrodes and surface of the drum. The electrodes are connected to ameans for successively applying a voltage pulse thereto having anamplitude less than that required to exceed the threshold voltagerequired for causing a discharge between the electrodes and a typecharacter on the drum. A second pulse, which, combined with thepreviously applied pulse exceeds the electrostatic discharge threshold,is applied to the electrodes selectively, as required, to cause a printout of the characters in accordance with data provided from a convenientsource.

This invention relates to systems for addressing high speed drum typeprinting systems and more particularly to improvements therein.

One of the high speed printing systems which is presently employed withdata processing machines comprises a rotatable drum or cylinder havingrows of characters dispersed around the periphery. At a writing station,there are placed a plurality of individually movable hammers. Betweenthe hammers and the drum periphery carbon paper and paper are passed.When it is desired to print on the paper, the hammers are selectivelyactuated to press the paper and carbon paper against the drum periphery.This causes an imprint of the letter or character opposite the actuatedhammer or hammers to be left on the paper.

The rotating printing drum usually has some associated arrangement foridentifying which row of letters or characters is coming into theprinting station. This identifying information is usually compared withthe information from a computer consisting of a line of letters to beprinted at a time. The line of letters to be printed is circulated oncefor comparison with each character in the printing station. In responseto an identity, the hammers located at corresponding positions in theline are actuated. It usually requires one cycle of the drum forprinting an entire line.

In an application by Rice and Frohbach Ser. No. 334,365, for a NonimpactDrum Printer, there is described a system which uses the circulatingdrum but, instead of having a plurality of selectively movable hammers,there are provided a plurality of conductive segments. In accordancewith that application, when a voltage pulse is applied between aconductive segment and the drum surface, there is deposited on thesurface of the paper an electrostatic charge pattern which has the shapeof the type font which is opposite the conductive segment at the time ofthe application of the voltage pulse. The paper is then moved to alocation at which the electrostatic image thereon is developed and fixedin accordance with well known xerograp'hic techniques.

Any addressing scheme for a printing drum must involve a storage meansfor holding information corre- 3,384,898 Patented May 21, 1968 spondingto one line of char-acters. If the printing drum is assumed to have arepertoire of 64 characters, with characters per line and if six binarybits are required for identifying each character, then the storagedevice must be capable of holding 6 l20=720 bits. Six 120-stage shiftregisters can be satisfactory as a storage device. During an intervalwhen the paper is advanced to a new line the computer or other inputdevice loads the 720 bits into the storage registers, and after that thedata is circulated continuously at a rate equal to or faster than onecomplete cycle per character row of drum rotation. This must be done,since during the time that one row of characters, say an A, is presentbefore the paper, the conductive segments corresponding to the positionson the line where the A is to be printed must be pulsed. The pulsesrequired are on the order of 600 to 1180 volts in amplitude (dependingon pulse duration and DC bias employed) so that the brute force solutionof using a separate high voltage pulse amplifier and computer for eachcharacter position is not too appealing.

An object of this invention is to provide a novel and unique addressingsystem for a noncontact drum printer of the general type described.

Yet another object of the present invention is to provide an addressingsystem for a noncontact drum printer of the type described wherein thenumber of pulse generators, comparators and amplifiers are considerablyreduced.

Still another object of the present invention is the provision of asimple addressing system for a noncontact printer of the type described.

These and other objects of this invention are achieved in a noncontactdrum printer by connecting the conductive bar segments which areemployed in applying voltage pulses, to successive taps along the delayline. The delay between taps is that required for adjacent characters ina row of type which row is skewed, to arrive at the printing position.In other words, in view of the skewing of the type font in a row, theentire row of type will not be present in the printing positionsimultaneously, but rather will appear therein successively one at atime. Skewing of type font on a drum type of printer is known andtaught, for example, in a patent to Hartley, No. 2,776,618.

A pulse is applied to one end of the delay line at the time that thesignals representative of the first character to be printed are appliedto the comparator. This pulse travels down the delay line raising thevoltage at each successive tap simultaneously with the arrivalthereunder of the type font in the skewed row of type on the surface ofthe drum. The amplitude of this voltage, however, is below the thresholdrequired to cause a charge pattern corresponding to the shape of thetype font to be deposited on the paper. The comparator compares theincoming signals representative of the characters in the line of typebeing scanned with signals from the reader for the type drum indicativeof the particular character which is in the printing position. When thecomparator indicates an identity, a second pulse generator is energizedto apply a pulse to all of the conductive segments. This pulse, is alsobelow the threshold value required for depositing an electrostaticcharge pattern on the paper. However, this pulse added to the voltagepulse on one or the taps corresponding to the position along the line oftype desired for printing, exceeds the threshold value and therefore,there will be deposited at the location indicated an electrostaticcharge pattern corresponding to the type font in the printing positionat the time of the pulse discharge.

In the second embodiment of the invention, the rows of type font neednot be skewed on the drum surface.

Here, the comparator energizes a pulse generator each time an identityis provided. The output of this pulse generator is applied to the tappeddelay line. Accordingly, a pulse pattern will exist in the delay line bythe time the row of type reaches the printing position, whichcorresponds to the desired ones of the type font it is desired to print.At this time, which is timed to occur at the end of a memory cycle ofcharacter representative signals received from the circulating memory, apulse is applied to all of the conductive segments such that the voltagethereon will exceed the treshold required for electrostatic depositionof charge on the paper. Alternatively, an opposite polarity pulse may beapplied to the drum at this time. As a result, there is a simultaneouscharge deposition along a line corresponding to those taps having avoltage thereon which exceeds the threshold required for theelectrostatic charge deposition.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself both as to its organization and method of operation, as well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIGURE 1 is a schematic diagram exemplifying the type of pressurelessprinting with which the addressing system of the present invention ismost suitable;

FIGURE 2 is a schematic drawing of a pressureless printing system inmore detail, with which the present invention finds its greatest use;

FIGURE 3 is a schematic drawing of one embodiment of this invention; and

FIGURE 4 is a schematic drawing of a second embodiment of thisinvention.

Referring now to FIGURE 1, there is shown a simple schematic drawing ofthe principles of non-contact printing, in order to afford a betterunderstanding of this invention. A conductive drum surface 10, shownfragmentarily in FIGURE 1, contains thereon an embossed raised type font12. Positioned opposite said type font 12 is a conductive segment 14.Paper on which it is desired to print is interposed between the typefont 12 and the conductive segment 14. The better the dielectricproperties of the paper, the longer the electrostatic charge patterndeposited thereon will remain undissipated.

A pulse source 16 is connected between the conductive segment 14 and theconductive drum surface 10. At the time that the drum surface positionsthe character 12 opposite the conductive segment 14, the pulse source isactuated by means, not shown, to apply a voltage between the drum andthe conductive segment. The type font 12 shapes the electric field whichis established therebetween so that a charge pattern is deposited on thesurface of the paper 14 having the shape of the type font. It should benoted that in order to obtain a charge deposition, a certain thresholdvoltage must be exceeded. It has been found that voltage pulses between600 and 1100 volts in amplitude, depending on pulse duration, and DCbias employed, must be applied in order to achieve electrostatic chargedeposition. Thus, a threshold of voltage above approximately 550 volts,may be said to exist. The paper on which the electrostatic charge imagehas been deposited is next moved to a developing and fixing station. Theelectrostatic charge image is developed and fixed in accordance withwell known xerographic techniques.

FIGURE 2 is a schematic drawing of a general arrangement forpressureless printing with which the present invention may be employed.A conductive drum 20, has the rows of type 22 disposed over the surfacethereof. The rows of type are shown as skewed, so that only one typefont in a row is within a printing position at any one instant, as thedrum rotates.

Usually, some form of identifying mechanism is employed to indicate thecharacter in a row of type font which reaches the printing position.This may be accomplished by an auxiliary drum 24 or disc which isrotated with the drum 20. A motor 26 may be employed for rotating thedrum and the disc 24. The disc contains the character code either by wayof embossing, engraving or magnetic deposition, which can be scanned bya reader 28 as the drum 24 is rotated, for producing signalsrepresentative of the character which is reaching the printing position.

A computer, not shown, supplies a line of character representativesignals, which are to be printed, to a circulating memory 30. Thecirculating memory circulates this line of character representativesignals and exposes signals representative of one character at a time inthe line sequence to a comparator 32. The comparator compares thesesignals with those received from the reader 28. Each time an identity isestablished, the identity signal is applied to the addressing circuits.It will be appreciated that it is necessary for the circulating memoryto circulate the line of character representative signals one completecycle for each row of type which passes under the printing position. Theprinting position is defined by a plurality of individual conductivesegments 34, one for each type font in a row of type. Each one of thesesegments 34 are identical to the segment 14 shown in FIGURE 1. Theprinting position is defined by the region between the plurality ofconductive segments 34 and the space opposite to them extending to thesurface of the drum. Each time the comparator 32 provides an outputsignal indicative of an identity between the signal received by thereader 28 and the line of character signals being circulated by thememory 30, addressing circuits 36 apply a voltage pulse between the drumand the one of the segments 34 opposite the location in linecorresponding to the location in the line of character signals which isdesired to be printed. In response to this voltage pulse, there is adeposition of electric charges on paper, not shown, which passes throughthe printing position between the conductive segment array and thesurface of the drum. While only nine conductive segments are showncorresponding to nine characters in a row of type, the usual drumprinter will have characters or, for that matter, any desired numbersince other than for reasons of practicality there is really nolimitation on the number which can be provided. Thus, if a pulseamplifier and/or pulse generator is required for driving each one of theconductive line segments 34, it will be appreciated that this canincrease the expense of the apparatus considerably.

In accordance with this invention, as shown in FIGURE 3, only two pulsegenerators need be employed for properly addressing the conductivesegments for printing. In FIG- URE 3, those structures which functionidentically to the structures in FIGURE 2 are given the same referencenumerals as are employed in FIGURE 2. When the circulating memory 30commences to circulate the signals representing a line of data desiredto be printed, the first character signal in said line of signals isemployed for exciting a pulse generator 40. The output of this pulsegenerator is applied to one end ofa tapped delay line 42. There are asmany taps on this delay line as there are conductive segments 34 whichit is desired to be driven. Each one of the conductive segments 34 isconnected to a separate one of the taps 42T on the delay line 42. Thedelay interval between the taps provided by the delay line 42corresponds to the time required to elapse between a type font which ispassing through the printing position and the adjacent and succeedingtype font in the skewed row to come into said printing position. Theamplitude of the voltage applied by the pulse generator 40 to one end ofthe delay line 42 is below the threshold necessary for deposition of anelectrostatic charge pattern on the paper in the printing position, saidpaper not being shown. Accordingly, as the drum 20 is rotated, a voltagepulse is applied to the plurality of conductive segments 34 successivelyas each type font in a row of type is opposite each conductive segment.The amplitude of this voltage pulse is below the threshold required forelectrostatic charge depositions.

Each time the comparator 32 determines that there is an identity betweenthe reader signal output and the circulating memory output, it appliesan identity signal to a second pulse generator 42. The output of pulsegenerator 42 is applied to every one of the conductor segments 34. Theoutput of pulse generator 42 alone is below the threshold of voltagerequired for electrostatic charge deposition. However, the output ofpulse generator 42 together with the pulse received from pulse generator40 is sufficient to exceed the voltage threshold.

Only the conductive segments 34 having the combination of a voltagepulse from the pulse generator 42 and a voltage pulse received from thetap on the delay line have a sufiicient voltage to exceed the requiredthreshold for electrostatic charge deposition on paper in the prlntmgposition. By way of a specific illustration, assume that the circulatingmemory 30 is circulating a line of character signals such that theletter A appears on the second and last positions of the line. When thecirculating memory first commences to circulate the line of charactersignals, the pulse generator 40 applies a pulse to the delay line 42.Assume now that a row of the letter A type has been recognized by thereader 28 as coming into the printing position. The pulse applied to thepulse generator will reach the second tap on the delay line 42 andtherefore will bias the second segment 34B when the second A type fontis in the printing position. By this time also, the circulating memoryhas applied a second set of character representative signals, thosespecifying an A to the comparator 32 whereupon the pulse generator 42 isexcited to apply a pulse to all of the conductive segments 34. Thisresults in the segment 34B having a voltage applied thereto whichexceeds the threshold and therefore electrostatic charge deposition willoccur on paper, not shown, which is in the printing position.

The circulating memory continues to circulate the line of data signals,the drum continues to rotate, and the pulse applied to the delay line 42continues to travel down the delay line. When the drum positions thelast type font A in the row of As in the printing position, the pulseapplied to the delay line 42 reaches the last tap and thus biases thelast one of the conductive segments 34L in the array. At this time also,if properly timed, the last set of character representative signals inthe line being circulated should be applied to the comparator 32. As aresult, the pulse generator 42 is excited and applies a pulse to all ofthe conductive segments including the last one 34L. The resultant twovoltages on this segment 34L exceed the voltage level required forcausing electrostatic charge deposition on the paper.

FIGURE 4 shows an alternative arrangement which may be employed toFIGURE 3. Here, it is not necessary that the rows of type be skewed onthe printing drum 20. Here, the comparator 32 applies an output pulse toa pulse generator 50 each time it senses an identity between the signalsapplied thereto by the circulating memory 30 and by the reader 28. Thepulse generator 50 applies its output to the tapped delay line 42. Itshould be noted at this point that the drum 24 is positioned relative tothe type rows on the drum 20 such that the reader 28 can indicate a rowof type just before it reaches the printing position. As a result, apulse pattern is established on the delay line 42 such that a voltage,which is less than the threshold voltage, is applied to each one of theconductive segments 34 in accordance with the ones of the charactersdesired to be printed. The circulating memory 30 also provides an outputat the completion of the circulation of a line of data which is appliedto a pulse generator 52. The output of this pulse generator is appliedto all of the conductive segments on the drum. This output is also lessthan the threshold value for electrostatic charge deposition, butexceeds the threshold value when combined with the voltage applied fromthe segments driven by the delay line taps. Thus, electrostatic chargedeposition is made to occur simultaneously over the entire row of typebut only at those locations where the particular character in theprinting position is specified in the line of data signals beingcirculated.

It should be appreciated that it is possible with this addressing systemto operate a plurality of printing stations simultaneously positionedaround the periphery of the drum, if the type repertoire is repeated anumber of times around the drum periphery. This can be done by repeatingthe conductive segments at the various locations around the drum toestablish printing stations thereat and by connecting the conductivesegments in parallel with one another. If, however, the drum only has asingle set of rows of type spaced around the periphery then multipleprinting can be effectuated by establishing a plurality of multipleprinting stations around the drum with conductive segments. A separateread head, however, is necessary here for detecting when a row of typeenters a specific printing position and a separate comparator for eachprinting position is required. However, these comparators can all besupplied by the output of the same circulating memory.

In the system shown in FIGURE 3, multiple stations are addressed byresistively connecting the conductive segments of every station to thesame delay line. Thus, each set of segments is synchronously scanned bythe same travelling pulse. The writing pulse is provided separately ateach station through a separate comparator and pulse source. The writingpulse is resistively coupled to all of the segments of its own writingstation. In the system shown in FIGURE 4, a separate delay line isrequired for each printing station. At the end of one cycle of thecirculating memory, the proper pulse pattern exists on each delay linecorresponding to the particular type row under each respective printingstation. At this instant the writing pulse is applied to all the tapssimultaneously, either by adding a pulse to all of the delay lines or bypulsing the drum itself.

There has accordingly been described and shown hereinabove a novel,useful system for addressing an electrostatic rum type printing system.

We claim:

1. The improvement in a high speed drum printer of the type wherein aplurality of aligned rows of type are dispersed about the periphery of adrum and an electrostatic printing location is established by aplurality of aligned conductive segments which are positioned adjacentthe periphery of said drum to establish therewith said printinglocation, each one of said segments being positioned to be aligned witha dilferent one of the type characters in each one of the rows of type,said improvement comprising means for applying first voltage pulses whena row of type is in said printing position between said drum and theones of said conductive segments which are opposite type characters insaid row which it is desired to print, each said first voltage pulsehaving an amplitude which is less than the amplitude required forelectrostatic charge deposition and a duration substantially equivalentto the time that a type character is opposite a conductive segment, saidmeans for applying first voltage pulses including a delay line having aplurality of taps therealong successively connected to successive onesof said conductive segments, means for applying first voltage pulses toone end of said delay line, and means for controlling the timing of theapplication of first pulses by said means for applyling pulses to makeeach pulse arrive at a tap on said delay line connected to a conductivesegment which is positioned opposite a type character desired to beprinted when said type character is in said printing location, and meansfor applying at the time a first pulse is applied to the one of saidconductive segments it is desired to print a second voltage pulsebetween said drum and all of said conductive segments having a durationsubstantially equivalent to the time that a type character is opposite aconductive segment, and an amplitude which is less than the amplituderequired for producing electrostatic charge deposition but which, whencombined with the first voltage pulse, exceeds the minimum amplituderequired for electrostatic charge deposition whereby an electrostaticcharge deposition corresponding to all the characters in a row desiredto be printed is made to occur during the interval required for a row oftype to pass through said printing location.

2. In a printing system of the type wherein a rotatable drum has rows oftype spaced around the periphery thereof and a printing position isestablished with the surface of said drum by a plurality of alignedconductive segments spaced opposite said drum each conductive segmentbeing associated with 'a different one of the type characters in a rowof type and being positioned so that the associated type characters passthereunder as said drum rotates, the improved means for addressing saidconductive segments for producing electrostatic charge depositions onpaper which is moved through said printing position comprisingmultitapped delay line means for successively applying over the intervalrequired for a row of type characters to pass through said printinglocation, a first voltage pulse between said drum and each of saidconductive segments within the interval that occurs as a type characterin a row of type with which a conductive segment is associated passesthrough the printing position, said first pulse having an amplitudevalue which is below that required to produce electrostatic chargedeposition, and means for applying only during the interval of a firstvoltage pulse a second voltage pulse between said drum and all of saidconductive segments which together with said first pulse raises thevoltage amplitude above that required for electrostatic chargedeposition at a time when it is desired to secure such electrostaticcharge deposition, whereby electrostatic charge deposition occurs forall of the characters in a row of type desired to be printed within theinterval required for said row to pass through said printing location.

3. The improvement recited in claim 2 wherein there is a meansconnecting each successive tap along said multitapped delay line meansto a successive one of said plurality of conductive segments, the delayprovided between taps of said multitapped delay line means beingdetermined as the transit time between type characters through saidprinting position, the connections between said conductive segments andthe taps on said delay line being arranged in a succession to establisha voltage on a conductive segment connected to a tap on said delay lineat the time that a type character is in said printing position oppositesaid conductive segment.

4. The improvement in a drum type printer wherein said drum has aplurality of rows of type characters dispersed around the peripherythereof and a plurality of conductive segments positioned adjacent saiddrum periphery established a printing station therebetween, each of saidconductive segments being aligned with a different one of said typecharacters in each row of type characters, said improvement comprisingmeans for circulating in their proper sequence character representativesignals indicative of a line of characters desired to be printed, meansresponsive to said drum rotation for providing identifying signalsrepresentative of a type character at said printing location, means forcomparing each of said character signals in said means for circulatingwith said identifying signals, multitapped delay line means responsiveto the first of said character representative signals in said means forcirculating for succesively applying over the interval required for arow of type characters to pass through said printing station a voltagepulse between said drum and all of said'conductive segments which has anamplitude less than that required to produce electrostatic chargedeposition and a duration determined by the interval that a typecharacter is at said printing station, means responsive to said meansfor comparing indicating an identity for applying a voltage pulsesimultaneously between said drum and all of said conductive segmentswhich has a duration on the order of one of said successively appliedvoltage pulses and an amplitude less than that required for producingelectrostatic charge deposition except when added to the voltage pulsebeing successively applied to said conductive segments, wherebyelectrostatic charge deposition occurs for all of the characters in arow of type desired to be printed within the interval required for saidrow to pass through said printing location.

5. The improvement in a drum type printer wherein said drum has aplurality of rows of type characters dispersed around the peripherythereof and a plurality of conductive segments positioned adjacent saiddrum periphery establish a printing station therebetween, each of saidconductive segments being aligned with a different one of said typecharacters in each row of type characters, the improvement comprisingmeans for circulating character signals representative of characters ina line of type desired to be printed, means for producing identifyingsignals representative of the type characters in a row on said drumperiphery before it reaches said printing position, means for comparingeach of said character representative signals to produce for eachidentity therebetween an identity output pulse having an amplitude lessthan that required for securing electrostatic charge deposition and aduration determined by the interval of alignment of a type character anda conductive segment, multitapped delay line means for applying withinthe interval that a row of type characters passes through said printingstation said identity pulses to those of said plurality of conductivesegments having a location from the first one thereof correspondingtothe location of the character signal which produces an identity signalfrom the first of the character signals in the line of charactersignals, means for producing a second voltage pulse having an amplitudeinsufficient to produce electrostatic, charge deposition except when itis added to the identity voltage pulse and a duration on the order ofthat of an identity output pulse, and means for applying said secondvoltage pulse to all of said conductive segments when the row of typecharacters, the identifying signal for which has been compared with theline of character signals, reaches said printing position, wherebyelectrostatic charge deposition occurs for all of the characters in arow of type desired to be printed within the interval required for saidrow to pass through said printing location.

References Cited UNITED STATES PATENTS 3,131,256 4/1964 Frohbach 346-743,188,649 6/1965 Preisinger 346-74 3,196,451 7/1965 Jones 346742,919,967 6/1957 SchWertZ 346--74 3,184,749 5 2/ 1962 Groth 346-743,208,076 5/1960 Mott 346-74 BERNARD KONICK, Primary Examiner.

T. W. FEARS, Examiner.

L. I. SCHROEDER, Assistant Examiner.

